1. Field of the Invention
The present invention relates to a storage controller and a control method of the storage controller.
2. Description of the Related Art
Various organizations such as a company, medical institution, government organization, and education institution use a storage controller in order to efficiently manage a large amount of data that increases on a daily basis. A storage controller stores important data such as sales data, customer data and research data, thus it is necessary to prepare for loss of data caused by human errors. Hedges against the loss of data include a method for creating a backup of a volume on a regular basis.
However, creating a backup and restoring data require a long time. Also, since data can be restored only when a backup is created, a data backup is not convenient. Therefore, as another hedge, there is known a first conventional technology in which a snapshot of a volume is created and journal data is acquired every time when the volume is updated, to manage the journal data (Japanese Unexamined Patent Publication No. 2005-18738). However, in this conventional technology as well, it is necessary to create a snapshot, and there is room for improvement in terms of convenience.
Therefore, there is also known a second conventional technology that allows restoration of data at any given point in time by using journal data (U.S. Patent Application Publication No. 2005/0028022).
The second conventional technology uses a data volume to be protected, a secondary volume to which storage contents of the protected data volume at some point in time are copied, and a journal volume that stores journal data. In the second conventional technology, at the time of restoration, data is copied from the secondary volume to the data volume to match the storage contents of the data volume to storage contents of the secondary volume. Next, in the second conventional technology, the journal data up until a specified time point is read out from the journal volume, and then written to the data volume. Therefore, according to the second conventional technology, data can be restored at any give point in time in increments of an update unit (in units of journal data).
However, when the capacity of the journal volume is fixed, the journal volume will eventually be filled with journal data, thus it is difficult to extend the period in which restoration can be performed. In the case of a configuration in which the capacity of the journal volume can be expanded, three is a risk that most of the storage capacity that the storage controller has is consumed in management of the journal data.
Furthermore, in the second conventional technology, the amount of data copied from the secondary volume to the data volume increases easily, thus it takes a long time to complete restoration.